Two-Dimensional Crystals of Alkanes Formed on Au(111) Surface in Neat Liquid:  Structural Investigation by Scanning Tunneling Microscopy

In situ scanning tunneling microscopy revealed the formation of the two-dimensional (2D) crystals of n-alkanes (CnH_[2n+2], n = 12-17) on a Au(111) surface in neat liquid at room temperature. The molecules were adsorbed on the gold surface with their molecular axis parallel to the surface plane. The molecular rows of even- and odd-numbered alkanes ran in the nearest-neighbor (NN) atomic direction and the next-nearest-neighbor atomic direction of the gold surface, respectively. The molecular axis was oriented close to the NN direction of the gold surface in both odd- and even-numbered alkanes. Although there are two NN directions with respect to the direction of the bridging row of the herringbone structure due to the reconstruction of the Au(111) surface with crossing angles of 30° and 90°, the molecular axis was preferentially oriented in the NN direction with a crossing angle of 30°. The 2D crystal of alkanes was not formed on the iodine-modified Au(111) surface, confirming that the molecule-substrate interaction played an important role in forming the 2D crystal of alkanes.